We plan to characterize the purified proteins involved in the mechanism of action of cyclic nucleotides in bovine cardiac muscle and to combine the information gained from studies in defined systems to that obtained using cells whose metabolic states can be manipulated and in which the tools of somatic cell genetics can be employed. It is hoped that the two approaches will be synergistic in furthering our understanding of cAMP-mediated protein phosphorylation reactions. The specific topics to be studied are: (1) Regulation of the principal soluble cAMP-dependent protein kinase (Type II) of bovine cardiac muscle, (2) structure, function and relationship of two cAMP-dependent protein kinases: Types I and II: (3) structure, function and regulation of the cGMP-dependent protein kinase of fetal calf cardiac muscle; (4) analysis of the heat- and acid-stable proteins that influence the activity of cyclic nucleotide-dependent protein kinases: (5) structure, function and regulation of muscle phosphoprotein phosphatases and (6) characterization of the structure of cyclic nucleotide phosphodiesterase and its induction by cAMP.